Some states means at least two, so yes, if you're asking if at least 2 out of 50 states allow this under certain conditions, the answer is probably yes. Those conditions may depend on:
1) the state
2) if you have the proper permit or licence
3) the type of fish
4) it's in season
5) if it's the right size and right sex
6) exactly where it's caught
7) exactly how it's caught
Any one of the above could make it illegal simply to catch the fish. Several of the above can make it illegal to keep the fish.
Keeping the fish you caught as a pet would almost always be illegal if it's illegal to possess the fish, e.g., since keeping certain fish (like piranha, snakeheads, etc.) is illegal in many states, you can't catch one and keep it.
Rather than digress on the issue of "wild" versus "domesticated" versus "feral" fish, I'd simply say that the laws describe the species, not the origins in this matter. A prohibited species doesn't become unprohibited to catch and keep because it's wild, domesticated or feral.
